1. Field of the Invention
This invention relates to superconductive photoconductive-substance of the Ca-Sr-Bi-Cu-O group system and a method for producing the same, which oxide has a composition outside that of a regular superconductor and exhibits a photoconductivity along with an either real or potential superconductivity.
As an outcome of experiments on optical properties, especially on the photoconductivity in response to high-speed laser pulses, of those oxides whose composition falls outside the critical composition range of a regular superconductor, the inventor has succeeded in finding a superconductive oxide of the Ca.sub.(X-x)-Sr.sub.x -Bi .sub.(Y-y)-Cu.sub.y -O.sub.z group that reveals photo-conductivity which is unexpected from the standpoint of conventional common sense. The invention is based on such findings.
The invention also relates to a method for producing the above oxide. In the method, the ingredient concentrations X, x, Y, y and z in the above-mentioned general formula are controlled, for instance by selecting X=2, Y=3, y=2, and a photoconductive oxide with an either real or potential superconductivity is produced by keeping the above concentration x close to zero in the 0.ltoreq.x&lt;1 range or by cooling extremely quickly. The oxide of the invention is expected to be very useful in the industrial field of "superconductive optoelectronics".
1. Related Art Statement
There have been no publications at all on such superconductor which has inherent photoconductivity, except the inventor's disclosure in his technical papers and his patent applications; for instance, a superconductive photoconductive oxide of the Y.sub.3-x)-Ba.sub.x -Cu.sub.y -O.sub.z group (U.S. patent application Ser. No. 244,240) and a superconductive photoconductive oxide of La.sub.2 -Cu.sub.y -O.sub.z group (U.S. Patent Application Serial No. 244,274).
Conventional superconductors are metals or alloys thereof in the main. Recently, much attention has been paid to high-temperature oxide superconductors, such as superconductors of the Y-Ba-Cu-O group, and considerable amounts of additives such as barium (Ba) and strontium (Sr) are used to raise the superconductive critical temperature (Tc). In view of the metallic properties of such a superconductive substance, studies and measurements on their optical properties at and in the proximity of visible wavelengths have been limited to the study of reflection and scattering of light therefrom as a part of the study on the overall nature of the metal.
In general, it has been believed that light is simply reflected from the surface of a superconductor and is not allowed to enter therein. Study of optical properties, except the phenomena of reflection and scattering, has been treated as a completely different field from that of superconductivity. This has been a main trend in academic institutions, domestic and abroad, and in international conferences.
The reason for the trend is in that researchers have considered that superconductivity is incompatible with such physical properties as light absorption and photoconductivity and they have assumed that light irradiation in a wave number with the excess energy over the energy gap of the BCS theory will merely destroy the stability of superconductivity. However, there is a certain clear correlation between them, as proven in the case of a Y-Ba-Cu-O group substance and the like. If any substance having both superconductive capability and photoconductive capability is produced, a number of new electronic and optoelectronic devices may be developed; for instance, a superconductive photo-transistor, a "superconductive optical computer" as a combination of the "superconductive computer" based on the Josephson devices and the "optical computer" proposed in optoelectronics both currently studied, "superconductive optical fiber" and the like